Many factors may contribute to fiber defects during melt spinning of fibers (K. V. Datye, A. A. Vaidya, Chemical Processing of Synthetic Fibers and Blends, John Wiley & Sons, New York, 1984, p 38). In particular, in the melt spinning of continuous multifilament synthetic yarns, malfunctions of the spinnerettes often produce enlarged sections in the yarn filaments which are known as "slubs" in yarn art language. These enlarged sections or "slubs" may also be produced by other malfunctions in the spinning process such as the breakage of filaments prior to or while they are being drafted. When a breakage of this type occurs, the broken filaments undergo no drafting in the spinning cabinet and thus an enlarged filament will result. Since the presence of these "slubs" appreciably detracts from the appearance, aesthetics and mechanical quality of the synthetic fiber structures being produced, it is extremely important to minimize or eliminate these defects.
The process of this invention unexpectedly allows the production of polyester fibers which have decreased "slub" formation and which, therefore, have improved quality and performance.
It is known that poly(1,4-cyclohexylene dimethylene terephthalate) (PCT) may be blended with conventional polyesters such as poly(ethylene terephthalate) and poly(butylene terephthalate) to lower the processing or extruding temperature of PCT to avoid degradation (Andrew B. Auerbach and Joseph W. Sell, Polymer Engineering and Science, 1990, Vol. 30, No. 17, pp 1041-1050).
British Pat. No. 1,344,492 discloses multicomponent filament fibers having high bulk prepared from at least two conjugated filamentary components in side-by-side relationship, one component (a) being formed from a homopolymer of ethyleneterephthalate (PET) and another component (b) being formed from a PET modified with 1,4-cyclohexanedimethanol as the reactive diol. There is no teaching of blending the polymeric components for components (a) and (b) and then spinning the polymer blends into filaments.
U.S. Pat. No. 4,668,764 easily dyeable polyester fibers comprising modified PET consisting of a copolyester having 80 to 98% of ethylene terephthalate units and wherein the monomer copolymerized with ethylene terephthalate is 1,4-cyclohexanedimethanol or 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane. There is no teaching of blending poly(ethylene terephthalate) with poly(ethylene terephthalate) modified with 1,4-cyclohexanedimethanol or the blending of two different poly(ethylene terephthalate) polymers modified with two different levels of 1,4-cyclohexanedimethanol with subsequent spinning into fibers.
U.S. Pat. No. 4,263,364 discloses that reinforced stampable thermoplastic polyester sheets are advantageously made by combining layers of PET film and PET modified with 1,4-cyclohexanedimethanol (copolyester) film and fiberglass followed by heating under pressure. No mention is made of combining the two polymers followed by spinning into fibers.
Research Disclosure, Vol. 252, No. 44 (No. 25244) discloses that certain blends of (1) poly(ethylene terephthalate) modified with 1,4-cyclohexanedimethanol (CHDM) with (2) other poly(ethylene terephthalate) modified with CHDM but which contains a different mole percent of CHDM are compatible if the difference in mole percent of CHDM is no greater than about 50%. There is no teaching as regards the use of these blends to prepare improved fibers and manufacturing efficiencies thereof.
U.S. Pat. No. 4,668,453 discloses a cospun yarn essentially free of defects comprising poly(hexamethylene adipamide/caproamide) (nylon 6,6/6) filament and certain modified poly(ethylene terephthalate) filaments.
No teaching is present in any of the references to lead one to combine two different poly(ethylene terephthalate) polymers modified with different levels of 1,4-cyclohexanedimethanol followed by melt spinning in an attempt to produce fibers having fewer spinning defects.